PROJECT SUMMARY/ABSTRACT This is an application for a K08 award for Dr. Jennifer Y. Chen, a gastroenterologist and hepatologist at the Massachusetts General Hospital (MGH). Dr. Chen?s long-term career goal is to become an independently funded physician scientist, devoting more than 75% of her time to establish and maintain a basic science research program in hepatic fibrosis. This K08 award will provide Dr. Chen with the support necessary to achieve her short-term goals: 1) develop additional training in molecular biology, including investigating protein interactions and induction of stable gene expression; 2) gain expertise in genome-wide transcriptional analysis; 3) become proficient in transgenic mouse work and mouse models of hepatic fibrosis; and 4) produce the data and publication record necessary for a successful R01 application. In prior work, the candidate has developed a small molecule screen to identify compounds that inactivate hepatic stellate cells (HSCs), the primary cell type responsible for hepatic fibrosis. Through analysis of a hit, she identified that the sphingolipid ceramide can profoundly inhibit the activated effector phenotype of HSCs. Her work has identified a potential antifibrotic role for inhibition of acid ceramidase (aCDase), the enzyme responsible for ceramide metabolism. In this proposal, the candidate seeks to elucidate the mechanism by which ceramide accumulation inactivates HSCs and define the role of aCDase in fibrosis progression. The specific goals of the study are to: 1) determine how ceramide mediates HSC inactivation; and 2) define the impact of aCDase depletion and inhibition on fibrosis development in vivo. Under the first aim, the applicant will utilize a combination of techniques including immunoblotting, small molecule inhibition and activation, RNA interference, and expression of constitutively activated mutant proteins to understand how ceramide inactivates HSCs. Genome-wide expression analysis will be performed to elucidate transcriptional targets of ceramide. Under the second aim, the applicant will generate mice with a conditional fibroblast-specific deletion of aCDase, and will determine the extent to which they experience reduced fibrosis in two independent models of hepatic fibrosis. She will also determine the antifibrotic effects of a small molecule inhibitor of aCDase in vivo. As an integral part of this proposal, the candidate?s career development will be complemented by participation in advanced coursework and research seminars to develop expertise in molecular biology, genome-wide transcriptional analysis, and in vivo models of hepatic fibrosis. A formal mentorship committee and advisory team will provide supervision, guidance, and assistance for the candidate to achieve her goals. The research environment, which includes the MGH GI Unit, Harvard Fibrosis Network, Harvard College, Harvard Medical School, and the Harvard School of Public Health, will provide a rich, collaborative, and supportive atmosphere to ensure the candidate?s success. Through this award, the candidate will become an independent basic science investigator by contributing to the understanding of the role of the sphingolipid ceramide and its inactivation of HSCs ex vivo and in vivo.